proc.5: Clarify the format of /proc/$PID/cmdline

It is possible to produce /proc/$PID/cmdline files which do not follow
the NUL-seperated format, by using the tricks described in the
paragraph below.

Signed-off-by: Günther Noack <gnoack@google.com>
[ fix semantic newlines ]
Signed-off-by: Alejandro Colomar <alx@kernel.org>

1 files changed, 13 insertions, 2 deletions

diff --git a/man5/proc.5 b/man5/proc.5
index a9bb175e8..723154edb 100644
--- a/man5/proc.5
+++ b/man5/proc.5
@@ -497,10 +497,21 @@ unless the process is a zombie.
 .\" In Linux 2.3.26, this also used to be true if the process was swapped out.
 In the latter case, there is nothing in this file:
 that is, a read on this file will return 0 characters.
-The command-line arguments appear in this file as a set of
-strings separated by null bytes (\[aq]\e0\[aq]),
+.IP
+For processes which are still running,
+the command-line arguments appear in this file
+in the same layout as they do in process memory:
+If the process is well-behaved,
+it is a set of strings separated by null bytes (\[aq]\e0\[aq]),
 with a further null byte after the last string.
 .IP
+This is the common case,
+but processes have the freedom to
+override the memory region and
+break assumptions about the contents or format of the
+.IR /proc/ pid /cmdline
+file.
+.IP
 If, after an
 .BR execve (2),
 the process modifies its